feat: quad shadows

wgpu/src/quad/solid.rs

@@ -105,6 +105,12 @@ impl Pipeline {
                             4 => Float32x4,
                             // Border width
                             5 => Float32,
+                            // Shadow color
+                            6 => Float32x4,
+                            // Shadow offset
+                            7 => Float32x2,
+                            // Shadow blur radius
+                            8 => Float32,
                         ),
                     }],
                 },